Imaging arrays are known in the art which comprise a transducer for either directly converting incident radiation to electrical charges, or for converting incident radiation to light energy (i.e. photons) and then converting the light energy to electrical charges. It is also known in the art to connect an active matrix read-out array to such prior art transducers, for collecting charges generated by the transducer onto individual pixels of the active matrix array, and then reading out the pixel charges on a row-by-row basis. The charge signals read out of the array are then measured using charge amplifiers connected to each source or data line. Examples of such prior art systems are disclosed in W. Zhao and J. A. Rowlands, "A Large Area Solid-State Detector for Radiology Using Amorphous Selenium", in Medical Imaging VI: Instrumentation, SPIE 1651, 134, (1992), and in L. E. Antonuk, J. Boudry, W. Huang , D. L. McShan, E. J. Morton, J. Yorkston, M. J. Longo and R. A. Street, "Demonstration of Megavoltage and Diagnostic X-ray Imaging with Hydrogenated Amorphous Silicon Arrays", Med. Phys. 19, 1455 (1992).
One disadvantage of prior art active matrix readout arrays is that each pixel is connected to a source line and a gate line of the associated switching transistor (e.g. thin film transistor (TFT)). This effectively reduces the fill factor for each pixel, unless an additional insulating layer is placed between the source lines or gate lines and the pixel electrodes.
Another disadvantage of prior art active matrix readout arrays is that it can be difficult and occasionally impossible to bond the arrays to external chips, when the gate our source line pitch is very small. Bonding technology is the main limiting factor in certain applications like mammography, where a pixel pitch as small as 50 microns is required. In mammography it is not possible to reduce the problem by bonding chips to every second line on both sides, since the active area on at least one side should be as close as possible to the chest wall and should not be bonded.
A further disadvantage of prior art active matrix readout arrays is that the charge amplifier design for such prior art arrays usually suffers from a trade-off between sensitivity and dynamic range. In particular, where a charge amplifier has been designed for high sensitivity in a prior art active matrix read-out array, such an amplifier is not capable of measuring large signals due to saturation of the response.